Composite comprising polymerized cyclic carbonate oligomer

ABSTRACT

A composition comprising a cyclic oligomer of the formula ##STR1## wherein X is selected from the group consisting of alkylene of two to twelve carbon atoms, inclusive, alkylidene of one to twelve carbon atoms, inclusive, cycloalkylene of four to twelve carbon atoms, inclusive cycloalkylidene of four to twelve carbon atoms, inclusive, ##STR2## a is zero or 1; n and m are the same or different and are integers of one to about fifteen; 
     R is alkylene of two to eight carbon atoms, inclusive or alkylidene of one to eight carbon atoms, inclusive, phenylene or a single bond. 
     R 1  and R 2  are the same or different and are alkyl or one to four carbon atoms, inclusive or halo; 
     b and c are the same or different and are integers of zero to four; and 
     R 3  and R 4  are the same or different and are alkyl of one to eight carbon atoms, inclusive, phenyl, hydrogen or R 3  and R 4  are taken together to form an alkylene of two to eight carbon atoms inclusive.

This is a division of copending application Ser. No. 796,985, filed11/12/85, now U.S. Pat. No. 4,701,538.

BACKGROUND OF THE INVENTION

Polycarbonates are well known polymers which have good propertyprofiles, particularly with respect to impact resistance, electricalproperties, dimensional rigidity and the like. These polymers aregenerally linear, but can be made with branched sites to enhance theirproperties in specific ways. Low levels of branching are generallyincorporated into the resin by co-polymerizing into the polymer backbonea tri or higher functional reagent to yield a thermoplasticpolycarbonate resin with enhanced rheological properties and meltstrength which make it particularly suitable for such types of polymerprocessing procedures as the blow molding of large, hollow containersand the extrusion of complex profile forms.

Sufficiently higher levels of branching sites in the resin will causeresin chains actually to join to each other to form partially or fullycrosslinked resin networks which will no longer be thermoplastic innature and which are expected to exhibit enhancements, overcorresponding linear resins, in physical properties and/or in theirresistance to abusive conditions, such as exposure to organic solvents.A wide variety of means have been employed to produce crosslinking inpolycarbonate resin. These generally involve the incorporation of asuitably reactive chemical group either into the resin chain at its timeof manufacture or as an additive to the resin after manufacture, orboth. These reactive groups and the reactions they undergo are generallydissimilar from those characteristic of polycarbonate resin itself andare therefore prone to have detrimental side effects on the physicaland/or chemical properties of the polymer. The conventional test used tojudge the success of these means for crosslinking is to observe theformation of gels due to the crosslinked material when a resin sample ismixed with a solvent, such as methylene chloride, in which normal linearpolycarbonate resin is highly soluble.

A new method has been discovered to prepare branched or crosslinkedpolycarbonate resin. This approach involves incorporating amultifunctional comonomer of better than two reactive groups into cyclicbisphenol carbonate oligomers. The thus prepared cyclic oligomers arethen reacted at elevated temperature with catalysis to yield highmolecular weight polycarbonate resin. Generally the polymerizationoccurs under melt conditions. This reaction is thought to proceed by amulti-step ring opening addition mechanism. During this polymerizationthe functional groups of the multifunctional comonomer are available forbuilding branches and/or for crosslinking one polycarbonate chain toanother polycarbonate chain.

This new method to prepare branched or crosslinked polycarbonate resinis an improvement over previous methods in that the resin is initiallylow in molecular weight and thus has low viscosity and is easilyprocessed into its desired forms. It is then converted under convenientreaction conditions to high viscosity branched resin or to cross-linkedresin. This is accomplished by incorporating into the resinmultifunctional comonomers with chemical groups with similar structureand reactivity to the repeat units of the resin so that the possibilityof detrimental side effects on resin properties are minimized.

SUMMARY OF THE INVENTION

In accordance with the invention, there is a composition comprising astructure of the formula ##STR3## wherein X is selected from the groupconsisting of alkylene of two to twelve carbon atoms, inclusive,alkylidene of one to twelve carbon atoms, inclusive, cycloalkylene offour to twelve carbon atoms, inclusive cycloalkylidene of four to twelvecarbon atoms, inclusive, ##STR4## a is zero or 1; n and m are the sameor different and are integers of one to about fifteen;

R is alkylene of two to eight carbon atoms, inclusive or alkylidene ofone to eight carbon atoms, inclusive, phenylene or a single bond.

R¹ and R² are the same or different and are alkyl or one to four carbonatoms, inclusive or halo;

b and c are the same or different and are integers of zero to four; and

R₃ and R₄ are the same or different and are alkyl of one to eight carbonatoms, inclusive, phenyl, hydrogen or R₃ and R₄ are taken together toform an alkylene of two to eight carbon atoms inclusive.

In further accordance with the invention, there is a compositioncomprising cyclic oligomers of Formula I in admixture with cyclicoligomers of the Formula II, the cyclic oligomer without a bridginggroup, ##STR5## wherein all the variables are defined as above. Examplesof the preparation and polymerization of cyclic oligomers are describedin copending Ser. Nos. 704,122, filed Feb. 22, 1985 and 723,672, filedApr. 16, 1985 and references contained therein, all of which areincorporated herein by reference.

The agent responsible for providing the crosslinking in the polymer is atetraphenol of the Formula ##STR6## wherein R, R³ and R⁴ are defined asabove.

Tetraphenols of Formula III can be incorporated into polycarbonate atlow levels using standard interfacial conditions to provide a branchedresin as described in U.S. Pat. No. 4,415,725. However, the levels oftetraphenol needed to achieve significant crosslinking and theproperties which ensue from crosslinking such as solvent resistance,will generally result in the formation of gels and/or extremely highviscosity resin. Such resins are difficult to convert to usefularticles. However, when compounds of Formula III are incorporated intocyclic oligomers of Formula I, these oligomers can be subsequentlypolymerized to form a crosslinked resin during in situ preparation ofuseful articles such as a fibrous reinforced material (composites). Sucharticles can be prepared by mixing or impregnating the fiber with thecyclic oligomers of this invention followed by thermal conversion tocrosslinked polymer.

The remainder of the polymer consists at least essentially of residuesof the dihydric phenol ##STR7## where X, R¹, R², a, b and c arepreviously defined in Formula Ia and Ib.

DESCRIPTION OF THE INVENTION

The incorporation of the compound(s) of Formula III into a bis cyclicoligomeric structure as shown in Formula Ia and Ib is done by theco-reaction of tetraphenols of Formula III with bisphenols of Formula IVby methods described below which yields mixtures of cyclic oligomers ofFormula II having a degree of polymerization of about 2 to 16 andbiscyclic oligomers of Formula Ia and/or Ib having a degree ofpolymerization in each ring of about 2 to 16.

The cyclic oligomers are mixtures generally having degrees ofpolymerization of from about 2 to about 15. Those compositions haverelatively low melting points as compared to single compounds such asthe corresponding cyclic trimer. The cyclic oligomer mixtures aregenerally liquid at temperatures above 300° C. and most often attemperatures above 225° C.

The mixtures useful in this invention contain very low proportions oflinear oligomers. In general, no more than about 10% by weight, and mostoften no more than about 5%, of such linear oligomers are present. Themixtures also contain low percentages (frequently less than 30% andpreferably no higher than about 20%) of polymers (linear or cyclic)having a degree of polymerization greater than about 32. Such polymersare frequently identified hereinafter as "high polymer". Theseproperties coupled with the relatively low melting points andviscosities of the cyclic oligomer mixtures, contribute to theirutility.

These mixtures can be prepared by a condensation reaction involving thetetraphenols of Formula III and the bishaloformates of the bisphenols ofFormula IV. These bishaloformates are shown in Formula V. ##STR8##wherein O-AR-O is the reaction residue of the dihydric phenols ofFormula IV reacted with phosgene or the bromo analogue. Halo is chloroor bromo and n is an integer of one to about six.

The cyclic oligomer forming reaction typically takes place interfaciallywhen a solution of said bishaloformate in a substantially non-polarorganic liquid is contacted with a tertiary amine from a specific classand an aqueous alkali metal hydroxide solution.

In one method for preparing the cyclic oligomer mixture, at least onesuch bishaloformate is contacted with at least one oleophilic aliphaticor heterocyclic tertiary amine and an aqueous alkaii metal hydroxidesolution having a concentration of about 0.1-10M, said contact beingeffected under conditions resulting in high dilution of bishaloformate,or the equivalent thereof, in a substantially non-polar organic liquidwhich forms a two-phase system with water; and subsequently, theresulting cyclic oligomer mixture is separated from at least a portionof the high polymer and insoluble material present.

The tertiary amines useful in the preparation of the cyclicpolycarbonate oligomers generally comprise those which are oleophilic(i.e., which are soluble in and highly active in organic media) and moreparticularly those which are useful for the formation of polycarbonates.Reference is made, for example, to the tertiary amines disclosed in theaforementioned U.S. Pat. No. 4,217,438 and in U.S. Pat. No. 4,368,315,the disclosure of which is also incorporated by reference herein. Theyinclude aliphatic amines such as triethylamine, tri-n-propylamine,diethyl-n- propylamine and tri-n-butylamine and highly nucleophilicheterocyclic amines such as 4-dimethylaminopyridine (which, for thepurposes of this invention, contains only one active amine group). Thepreferred amines are those which dissolve preferentially in the organicphase of the reaction system; that is, for which the organicaqueouspartition coefficient is greater than 1. This is true because intimatecontact between the amine and bischloroformate is essential for theformation of the cyclic oligomer mixture. For the most part, such aminescontain at least about 6 and preferably about 6-14 carbon atoms.

The most useful amines are trialkylamines containing no branching on thecarbon atoms in the 1- and 2- positions. Especially preferred aretri-n-alkylamines in which the alkyl groups contain up to about 4 carbonaooms. Triethylamine is most preferred by reason of its particularavailability, low cost, and effectiveness in the preparation of productscontaining low percentages of linear oligomers and high polymers.

The aqueous alkali metal hydroxide solution is most often lithium,sodium or potassium hydroxide, with sodium hydroxide being preferredbecause of its availability and relatively low cost. The concentrationof said solution is about 0.2-10M and preferably no higher than about3-5M.

The fourth component in the cyclic oligomer preparation method is asubstantially non-polar organic liquid which forms a two-phase systemwith water. The identity of the liquid is not critical, provided itpossesses the stated properties. Illustrative liquids are aromatichydrocarbons such as toluene and xylene; substituted aromatichydrocarbons such as chlorobenzene, o-dichlorobenzene and nitrobenzene;chlorinated aliphatic hydrocarbons such as chloroform and methylenechloride; and mixtures of the foregoing with ethers such astetrahydrofuran.

To prepare the cyclic oligomer mixture according to the above-describedmethod, the reagents and components are maintained in contact underconditions wherein the bischloroformate is present in high dilution, orequivalent conditions. Actual high dilution conditions, requiring alarge proportion of organic liquid, may be employed but are usually notpreferred for cost and convenience reasons. Instead, simulated highdilution conditions known to those skilled in the art may be employed.For example, in one embodiment of the method the bischloroformate or amixture thereof with the amine is added gradually to a mixture of theother materials. It is within the scope of this embodiment toincorporate the amine in the mixture to which the bischloroformate isadded, or to add it gradually, either in admixture with the amine orseparately. Continuous or incremental addition of the amine isfrequently preferred, whereupon the cyclic oligomer mixture is obtainedin relatively pure form and in high yield.

Although addition of the bischloroformate neat (i.e., without solvents)is within the scope of this embodiment, it is frequently inconvenientbecause many bischloroformates are solids. Therefore, it is preferablyadded as a solution in a portion of the organic liquid. The proportionof organic liquid used for this purpose is not critical; about 20-80% byweight, and especially about 40-60%, is preferred.

The reaction temperature is generally in the range of about 0°-50° C. Itis most often about 0°-40° C. and preferably 20°-40° C.

For maximization of the yield and purity of cyclic oligomers as opposedto high polymer and insoluble and/or interactable by-products, it ispreferred to use not more than about 0.7 mole of bischloroformate perliter of organic liquid present in the reaction system, including anyliquid used to dissolve said bischloroformate. Preferably, about0.003-0.6 mole of bischloroformate is used. It should be noted that thisis not a molar concentration in the organic liquid when thebischloroformate is added gradually, since it is consumed as it is addedto the reaction system.

The molar proportions of the reagents constitute another importantfeature for yield and purity maximization. The preferred molar ratio ofamine to bischloroformate is about 0.1-1.0:1 and most often about0.2-0.6:1. The preferred molar ratio of alkali metal hydroxide tobischloroformate is about 1.5-3:1 and most often about 2-3:1.

Step II of the cyclic oligomer preparation method is the separation ofthe oligomer mixture from at least a portion of the high polymer andinsoluble material present. When the other reagents are added to thealkali metal hydroxide and the preferred conditions and materialproportions are otherwise employed, the cyclic oligomer mixture(obtained as a solution in the organic liquid) typically contains lessthan 30% by weight and frequently less than about 20% of high polymerand insoluble material. When all of the preferred conditions areemployed, the product may contain 10% or even less of such material.Depending on the intended use of the cyclic oligomer mixture, theseparation step may then be unnecessary.

Therefore, a highly preferred method for preparing the cyclic oligomermixture comprises the single step of conducting the reaction using asthe amine at least one aliphatic or heterocyclic tertiary amine which,under the reaction conditions, dissolves preferentially in the organicphase of the reaction system, and gradually adding bischloroformate,amine and alkali metal hydroxide simultaneously to a substantiallynon-polar organic liquid or a mixture of said liquid with water, saidliquid or mixture being maintained at a temperature in the range ofabout 0°-50° C.; the amount of bischloroformate used being up to about0.7 mole for each liter of said organic liquid present in the reactionsystem, and the molar proportions of amine and alkali metal hydroxide tobischloroformate being 0.2-1.0:1 and 2-3:1, respectively althoughgreater quantities of amine or alkali hydroxide can be employed ifdesired; and recovering the cyclic oligomers thus formed.

As in the embodiment previously described, another portion of saidliquid may serve as a solvent for the bischloroformate. Addition of eachreagent is preferably continuous, but may be incremental for any or allof said reagents.

In preparation of oligomers some of the carbonate linkages can bereplaced with ester linkages by use of ester containing bisphenolprecursors such as the reactor product of greater than one mole ofbisphenol with one mole of a diacid chloride, such as terephthaloylchloride and/or isophthaloyl chloride in the formulation of the cyclicoligomers. In this manner aromatic copolyester carbonate oligomers canbe prepared wherein up to all but one of the carbonate units has beenreplaced by an aromatic carboxylic ester unit.

When a separation step is necessary, the unwanted impurities may beremoved in the necessary amounts by conventional operations such ascombining the solution with a non-solvent for said impurities.Illustrative non-solvents include ketones such as acetone and methylisobutyl ketone, esters such as methyl acetate and ethyl acetate andalcohols such as isopropanol or isobutanol. Acetone is a particularlypreferred non-solvent. Recovery of the cyclic oligomers normally meansmerely separating the same from diluent (by known methods such as vacuumevaporation) and, optionally, from high polymer and other impurities.

With respect to the structure of the formulae, X is preferably alkyleneof two to six carbon atoms, inclusive, alkylidene of one to six carbonatoms, inclusive, cyclalkylidene of six to twelve carbon atoms,inclusive, ##STR9## a is preferably 1. R is preferably alkylene of twoto four carbon atoms, inclusive or alkylidene of one to four carbonatoms, inclusive.

R¹ and R² are the same or different and are preferably alkyl of one tothree carbon atoms, inclusive, chloro or bromo.

b and c are the same or different and are preferably 0, 1 or 2.

R₃ and R₄ are the same or different and alkyl of one to four carbonatoms, inclusive or taken together form an alkylene of two to fourcarbon atoms, inclusive.

The cyclic oligomers are converted to high molecular weight polymers bystandard reaction conditions utilizing transesterification typecatalysts. Generally tranesterifications are carried out in the meltstate in general accordance with known processes described, inter alia,in The Encyclopedia of Polymer Science, Vols. 9 and 10 (1969); Chemistryand Physics of Polycarbonates, H. Schnell, Vol. 9, John Wiley and Sons,Inc. (1964); Polycarbonates, Christopher and Fox, Reinhold Corporation,(1962); U.S. Pat. No. 4,217,438; U.S. Pat. No. 4,329,443 and U.S. Pat.No. 4,217,438, all of which are hereby incorporated by reference.

The transesterification catalysts used in the preparation of the instantpolycarbonates are any of the well known and conventionaltransesterification catalysts. These catalysts include the organic andinorganic bases, the organic and inorganic protic acids, and the Lewisacids. Some illustrative non-limiting examples of organic and inorganicbase catalysts include sodium metal, lithium hydroxide, sodiumcarbqnate, sodium acetate, sodium methylate, sodium borohydride,isopropylamine, pyridine, sodium benzoate, sodium phenoxide, sodiumaluminumhydride, and sodium borohydride. Some illustrative non-limitingexamples of protic acid catalysts include hydrochloric acid,hydrofluoric acid, hydrobromic acid, sulfuric acid, sulfonic acid,methanesulfonic acid, benzene sulfonic acid, and phosphonic acid. Someillustrative non-limiting examples of Lewis acid catalysts includeborontrifluoride, stannic chloride, and dialkyl tin oxide. Other Lewisacid catalysts are disclosed, inter alia, in U.S. Pat. Nos. 4,045,464,3,255,236, and 4,182,726, all of which are incorporated herein byreference. Other protic acid catalysts are disclosed, inter alia, inU.S. Pat. No. 3,767,648, which is incorporated herein by reference.

The amount of the catalyst employed is a catalytic amount. By catalyticamount is meant an amount effective to catalyze the reaction. Generally,molar ratios of catalyst to dihydric phenol in the range of from about1×10⁻⁵ to 1 to about 1×10⁻¹ to 1 can be used.

The crosslinking which occurs in the polycarbonates is generallyphysically manifested by the appearance of gels when the polycarbonateplaced in an organic solvent such as methylene chloride. Thenoncrosslinked polycarbonate will go into solution; the crosslinkedpolycarbonate will remain in gel form.

The crosslinked residue and useful articles made from this invention mayoptionally contain the commonly known and used additives such as, forexample, antioxidants, mineral fillers, reinforcing agents, impactmodifiers, colorants, ultraviolet radiation absorbers such as thebenzophenones, benzotriazoles, and cyanoacrylates; color stabilizerssuch as the organophosphites described in U.S. Pat. Nos. 3,305,520 and4,118,370, both of which are incorporated herein by reference;hydrolytic stabilizers such as the epoxides described in U.S. Pat. Nos.3,489,716; 4,138,716 and 3,839,247, all of which are incorporated hereinby reference, and flame retardants.

Some particularly useful reinforcing agents which may be used separatelyor in combination are carbon, aramid, glass and boron fibers and otherreinforcements which may be chopped, woven, knit, braided, wound orshaped by any conventional method.

Some particularly useful flame retardants are the alkali and alkalineearth metal salts of organic sulfonic acids. These types of flameretardants are disclosed, inter alia, in U.S. Pat. Nos. 3,933,734;3,938,851; 3,926,908, 3,919,167; 3,909,940, 3,853,396; 3,931,100;3,978,024; 3,953,399; 3,917,599, 3,951,910 and 3,940,366, all of whichare incorporated herein by reference.

The following are examples. These examples are intended to illustratethe embodiments within the inventive concept. The examples are not meantto narrow the inventive concept.

EXAMPLE 1 PREPARATION AND POLYMERIZATION OF A 2 MOLE % CYCLIC OLIGOMERCOPOLYMER UTILIZING 4,4',4",4'"-(1,4-DIMETHYLBUTANEDIYLIDENE)TETRAPHENOL

a. Preparation of bischloroformate oligomers. A 1000 ml four neck flaskwas fitted with a mechanical stirrer, a pH probe, an aqueous causticinlet tube and a Claisen adapter to which was attached a dry icecondenser and a gas inlet tube. To the flask was added 200 ml ofmethylene chloride, 200 ml water and 43.8 g (0.192 mole) of bisphenol-A.

To the flask was then added phosgene at 2.0 g/min for 21 minutes (42 g,0.42 mole) with the pH maintained in the range 2 to 5 by addition of 25wt. % aqueous sodium hydroxide. After completion of phosgene addition,the reaction mixture was stirred for an additional 15 minutes, and themethylene chloride layer was removed. The methylene chloride solutionwas used directly in the cyclization reaction.

b. Cyclization of the bischloroformate oligomers. A 1000 ml flask wasfitted with a mechanical stirrer and an addition funnel containing thebischloroformate oligomer solution prepared above. To the flask wasadded 40 g of 50% aqueous sodium hydroxide, 160 ml water, 300 mlmethylene chloride, 6.4 ml (0.046 mole) triethylamine and 1.82 g (0.004mole) of 4,4',4",4'"-(1,4-dimethylbutanediylidene)tetraphenol. Thebischloroformate oligomer solution was then added drop wise over onehour to the slowly stirred reaction mixture. The reaction mixture wasstirred an additional 15 minutes and then quenched with 3N aqueous HClto pH of 3. In a separatory funnel, the methylene chloride solutionlayer was separated from the aqueous layer and from a layer of gels,then washed with 200 ml of 0.01M aqueous HCl, then washed with 200 ml ofdistilled water, dried over MgSO₄, filtered and the solvent removedunder vacuum to yield 41 g of a white solid. To that solid was thenadded 500 ml acetone. The resultant slurry was stirred for 30 minutes,then filtered and the solvent removed under vacuum to yield 33.5 g ofthe acetone - soluble cyclic oligomers, which were then used directly inthe polymerization reaction.

c. Polymerization of the cyclic oliqomers. To 5.0 g (2.0×10⁻² mole) ofthe cyclic oligomers from above dissolved in 25 ml methylene chloridewas added 0.0038 g (1×10⁻⁵ mole) tetramethylammonium tetraphenyl boratedispensed in 5 ml methylene chloride. The solvent was then removed undervacuum and the resultant residue dried for 4 hours at 120° C. Themixture was then compression molded at 250° C. for 20 minutes into a 1.5inch diameter disk.

A 1.86 g sample from the disk was then swelled in 40 ml methylenechloride and the resultant gel repeatedly soaked and washed withmethylene chloride until no additional soluble resin was observed to beremoved from the gel. The gel was then dried and weighed (1.77 g, 95%).

EXAMPLE 2 PREPARATION AND POLYMERIZATION OF A 4 MOLE % CYCLIC OLIGOMERCOPOLYMER UTILIZING 4,4',4",4'"-(1,4-DIMETHYLBUTANEDIYLDENE)TETRAPHENOL

The same procedures as described above in Example 1 were used, startingwith 42.9 g (0.184 mole) bis-phenol-A and 3.64 g (0.008 mole)4,4',4",4'"-(1,4-dimethylbutanediylidene)tetraphenol. The yield of crudeproduct was 37.6 g and of the acetone - soluble portion 29 g.

The resultant resin exhibited 90% gels.

PREPARATION OF CONTROL SAMPLE

A sample was prepared essentially by the same procedure as above usingbisphenol-A and no tetraphenol co-monomer. It exhibited 3.0% gels.

What is claimed is:
 1. A composite material comprising a fibrous ormatted material having added to or impregnated thereon at least oneliquid cyclic oligomer of the formula ##STR10## wherein X is selectedfrom the group consisting of alkylene of two to twelve carbon atoms,inclusive, alkylidene of one to twelve carbon atoms, inclusive,cycloalkylene of four to twelve carbon atoms, inclusive, cylcoalkylideneof four to twelve carbon atoms, inclusive, ##STR11## a is zero or 1; nand m are the same or different and are integers of one to aboutfifteen;R is alkylene of two to eight carbon atoms, inclusive oralkylidene of one to eight carbon atoms, inclusive, phenylene or R is asingle bond; R¹ and R² are the same or different and are alkyl or one tofour carbon atoms, inclusive or halo; b and c are the same or differentand are integers of zero to four; and R₃ and R₄ are the same ordifferent and are alkyl of one to eight carbon atoms, inclusive, phenyl,hydrogen or R₃ and R₄ are taken together to form an alkylene of two toeight carbon atoms inclusive.
 2. The composite material of claim 1wherein the cyclic oligomer has been polymerized in situ and is now highmolecular weight aromatic polycarbonate.
 3. A composite materialcomprising a fibrous or matted material having added to or impregnatedthereon at least one cyclic oligomer of the formula ##STR12## wherein Xis selected from the group consisting of alkylene of two to twelvecarbon atoms, inclusive, alkylidene of one to twelve carbon atoms,inclusive, cycloalkylene of four to twelve carbon atoms, inclusive,cycloalkylidene of four to twelve carbon atoms, inclusive, ##STR13## ais zero or 1; n and m are the same or different and are integers of oneto about fifteen;R is alkylene of two to eight carbon atoms, inclusiveor alkylidene of one to eight carbon atoms, inclusive, phenylene or R isa single bond; R¹ and R² are the same or different and are alkyl or oneto four carbon atoms, inclusive or halo; b and c are the same ordifferent and are integers of zero to four; and R₃ and R₄ are the sameor different and are alkyl of one to eight carbon atoms, inclusive,phenyl, hydrogen or R₃ and R₄ are taken together to form an alkylene oftwo to eight carbon atoms inclusive.
 4. The composite material of claim3 wherein the cyclic oligomer has been polymerized in situ and is nowhigh molecular weight aromatic polycarbonate.